Journal of Materials in Civil Engineering

Fatigue cracks were observed in the 1800s in steel structures—bridge and railroad—in Europe because of cyclic loading; since then, fatigue has been extensively studied in various fields. Several techniques, approaches, and criteria were developed to achieve this purpose. The first fatigue study on hot mix asphalt (HMA) was performed at Nottingham University in the 1950s; since then, a massive amount of work has been done. This paper provides a review survey of fatigue studies of asphalt mixtures; this survey includes demonstrating fatigue test techniques, test modes, load configurations, approaches, and criteria. These approaches range from simple, such as the traditional approach, to complex, such as the mechanistic approach, and can be used in evaluating the fatigue performance of asphalt binders and mixtures, except for the linear amplitude sweep (LAS) test, which is used only for binder and mastic. A French approach was developed to depict asphalt fatigue performance only from a pure fatigue damage perspective without due regard to other artifacts that occur during the fatigue damage process.

Wood is one of the most advantageous structural materials available today because of its renewability, natural carbon sequestration, affordability, and relative ease to construct. Unfortunately, this ease of fabrication makes it possible to change wood structures in the field without extensive review and planning. Forensic studies have pointed to poor construction execution or material specification. Thus, as part of a Structural Engineering Institute (SEI)-funded special project awarded to the SEI Performance of Wood Structures Committee to lead towards the development of a standard of practice for the performance of wood structures, this paper examines the role of damage mechanisms caused by decay fungi through the review of the state of the art in research regarding common wood-affecting fungal species in the US. While a properly designed and constructed building envelope is most important, techniques in both the identification and prevention of fungal wood decay are reviewed in this paper as leverage in the development of a standard of practice for wood structures for design, construction, and service.

The bond-slip relationship is determined from the measured load and the measured relative displacement between the rebar and the concrete in a pullout test. It is considered a characteristic constitutive property of the rebar–concrete, interface and in standards and manuals it is commonly described by a single nondimensional bond stress-slip curve. It is well known that the actual bond-slip relationship depends on the concrete uniaxial compressive strength. Examination of the results of many pullout experiments on normal-strength concrete specimens conducted for the present study indicates that numerous bond-slip curves do not follow the expected single nondimensional curve. Analysis of available data clearly shows two typical normalized bond-slip curves that differ mainly in the slope of the descending branch and the residual bond stress at large values of slip. A series of complementary pullout tests has been conducted for validation and for further analysis of the results. Results of these tests clearly show the two basic bond-slip curve forms, supporting the foregoing observations. Examination of the internal cracking and local damage in the tested specimens at the end of each experiment indicates that the two different curve forms are related to different internal damage mechanisms, which depend on the concrete tensile strength.

Different methods are available to quantify the fatigue damage of the asphalt mixtures. Among these, methods based on the concept of dissipated energy are used predominantly. Characterizing fatigue damage using the concept of dissipated energy is complicated due to the presence of other modes of dissipation, for instance, viscous dissipation. Hence, most of the investigations attempt to separate the dissipation due to damage from the viscous dissipation. One of the widely used approaches to separate fatigue dissipation involves the use of a parameter called pseudostrain. The area under the stress-pseudostrain curve, called the dissipated pseudostrain energy, is used to characterize fatigue. In this study, the usefulness or otherwise of this approach to separate fatigue and viscous dissipation is explored. Toward this, experimental investigations were conducted using four-point bending for four types of asphalt mixtures at two different temperatures and four strain levels. It was observed that although the concept of pseudostrain to characterize the fatigue damage holds good in some specific cases, it cannot be adopted for all experimental data collected in this study. In view of this, a new strategy to separate the total dissipation into viscous and fatigue dissipation is proposed based on a constitutive assumption for the viscous dissipation of damaged asphalt concrete. This new method is then used to quantify fatigue damage in this study.

Surface charge properties of colloids can be studied from their point of zero charge (PZC) measurements. The point of zero salt effect (PZSE), a category of PZC, indicates the pH value at which the effect of electrolyte concentration on a pH-dependent charge is zero. In the present study, it was mathematically deduced that for clay minerals, the rate change of pH and zeta potential with ionic concentration approaches zero at a pH value corresponding to the PZSE of the soil. The procedure is based on applying the constraint of electroneutrality to the charge-balance equation for colloids in equilibrium with an electrolyte. The theoretical observations were corroborated experimentally by obtaining the pH and zeta potential variations of three mineralogically diverse soils and comparing the values with the standard salt titration results. The study identifies PZSE from pH measurement as a more suitable approach for soil exhibiting variable charge. In the case of highly reactive soils, PZSE measurement using a divalent electrolyte medium yielded comparable results. In view of the obtained results, the proposed method can be an alternative for PZSE determination of clay minerals.

Sustained loading has an important impact on concrete structures in service due to deteriorations of material properties and degradations of durability. Sustained loading and three-point bending (TPB) tests were carried out to study the influence of long-term loading on the fracture of concrete. The specimens were firstly tested under three load levels, i.e., 30% and 60% of the maximum load and the crack initiation load over 30 days. After that, these specimens were removed from the loading frames and immediately loaded up to failure under static TPB loading. The critical crack propagation length ($\mathrm{\Delta }{a}_{\mathrm{c}}$), the initial cracking load ($P_{\mathrm{ini}}$), the peak load ($P_{\max }$), and the fracture energy ($G_{\mathrm{f}}$) were obtained in the TPB tests. Accordingly, the initial fracture toughness ($K_{\mathrm{IC}}^{\mathrm{ini}}$), the unstable fracture toughness ($K_{\mathrm{IC}}^{\mathrm{un}}$) and the evolution of stress intensity factors (SIFs) were determined by considering the stress relaxation at the precrack tip. Furthermore, the fracture properties of concrete affected by the long-term loading can be obtained by comparing with those from the static TPB tests. The results indicated that the stress relaxation at the precrack tip caused by the viscoelasticity of concrete led to the increases in $P_{\mathrm{ini}}$ and $P_{\max }$ but had almost no effects on $\mathrm{\Delta }{a}_{\mathrm{c}}$ and $G_{\mathrm{f}}$. The formula for calculating $K_{\mathrm{IC}}^{\mathrm{ini}}$ and $K_{\mathrm{IC}}^{\mathrm{un}}$ from linear elastic fracture mechanics would no longer be appropriate for those creep specimens and would overestimate the values of $K_{\mathrm{IC}}^{\mathrm{ini}}$ and $K_{\mathrm{IC}}^{\mathrm{un}}$. By taking into account the stress relaxation, the calculated values of $K_{\mathrm{IC}}^{\mathrm{ini}}$ and $K_{\mathrm{IC}}^{\mathrm{un}}$ for the creep specimens were almost the same as those under the static loading. Therefore, the values of $K_{\mathrm{IC}}^{\mathrm{ini}}$ and $K_{\mathrm{IC}}^{\mathrm{un}}$ derived from the static TPB tests can still be used to evaluate the cracking resistance of concrete materials and the stability of concrete structures under different load levels.

The evolution of morphology at the microscale of polymer-modified asphalt under thermal conditions is of interest due to its great influence on the macroperformance of asphalt. In this paper, a phase-field method is presented to model the evolution of microstructure and storage stability of ethylene-vinyl acetate (EVA)-modified asphalt. The influence of vinyl acetate (VA) on phase-separation behavior and storage stability of EVA-modified asphalt was evaluated by the combination of simulation and experiment. The diffusion, interaction, and swelling between polymer and asphalt matrix were analyzed. The results indicated that the phase field in two dimensions describes the evolution of morphology observed from fluorescence microscopy for EVA-modified asphalt under isothermal annealing conditions. Diffusion and the interface between EVA molecules and asphalt mainly control the phase-separation behavior. Higher VA content causes less diffusion and promotes interaction and swelling between EVA and asphalt matrix. The storage stability predicted by the coupled Navier-Stokes phase-field model (NSPFM) indicated that phase separation becomes slower with the increase of VA, which is affected by the difference in density between polymer and asphalt. The stability results predicted by NSPFM were validated with fluorescence microscopy and tube test results.

In this study, the author proposes two methods for estimating the permeability of sand and gravel from their pore structure. First, the author proposes a model to be used in both methods for estimating the pore-size distribution based on the concept of the probability of particles’ contact with one another in consideration of the number of particles for different particle sizes calculated from the particle-size distribution. In one method, the author defines an index of the threshold pore size around which the cumulative pore size increases rapidly in the obtained pore-size distribution model. Then, a semiempirical formula is proposed for evaluating the permeability. Here, by taking the power of the threshold pore size as the key parameter, the relationship between permeability and threshold pore size can be expressed as a linear function. In the other method, the author proposes a theoretical formula for estimating the permeability from the Hagen-Poiseuille flow equation using the proposed pore-size distribution model. Comparison with test measurements demonstrates that the calculations obtained from the proposed methods using the pore-size distribution agreed well with the test measurements, whereas those obtained from the existing methods directly using the particle-size distribution did not.

Epoxy asphalt is a thermosetting paving material that can provide higher strength, stiffness, adhesion, high-temperature stability, and service life compared to conventional asphalt; however, it has not been widely used on highway pavements, primarily due to the higher initial cost and limited operational window. In this paper, dilution of epoxy asphalt with styrene-butadiene-styrene (SBS)-modified asphalt was studied for the potential use in chip seal applications. Performance characteristics such as workability, hardening process, uncured and fully cured bond strength, and fully cured binder performance in both high and low temperatures were also investigated thoroughly. It was found that the SBS-modified asphalt has a higher initial adhesion feature and can help provide a quicker opening to traffic after construction than the undiluted epoxy asphalt. Meanwhile, epoxy asphalt binder in the blend can enhance the final adhesive strengths to retain the chips under strain induced by vehicles in the long term. The dilution level in $1:0.5$ and $1:1$ ratios showed a faster polymerization/curing rate than the $1:2$ and $1:3$ ratios. Diluted epoxy asphalt also showed improved low-temperature performance compared to undiluted epoxy asphalt and better high-temperature performance compared to pure SBS-modified asphalt. Overall, this paper presents that dilution of epoxy asphalt with SBS-modified asphalt could have significant practical benefits, and the $1:1$ dilution ratio seems to be the most suitable from the aspects of performance, cost, and practical use.

Collapsible soils such as loess, which are naturally unsaturated, are a type of problematic soil that has high resistance in dry conditions but when wet and saturated suddenly collapses, creating hazards for structures built on them. Therefore, the stabilization of such soils with cement can be effective. Because cement production is costly and one of the most important causes of air pollution in the world, replacing a portion of cement with an environmentally friendly additive such as natural zeolite (NZ) is of great importance. The present study aimed to quantify the influence of cement and zeolite as well as recycled polyester fiber (PET) on the unconfined compressive strength (UCS) of loess soil using a series of unconfined compression tests. The results indicated that the UCS of samples stabilized with 4% and 8% cement were substantially enhanced by increasing zeolite replacement to an optimum value of 10% and 30%, respectively. The highest resistance was achieved in mixtures with a water content ($\omega$) equal to 1.2 times optimum water content (${\omega }_{\mathrm{opt}}$). Additionally, soil stabilization with a combination of cement, zeolite, and recycled polyester fiber significantly increased UCS. The addition of PET to a zeolite-cement-loess mixture caused an increase in failure strain. To overcome the brittle behavior of cemented loess, the combination of PET and zeolite in a cement-loess mixture is very effective.

This study explores the possibility of using alkali lignin as a soil stabilizer as well as the possibility of polymerizing alkali lignin to further improve its performance. The polymerization involves cross-linking phenoxy radicals of lignin precursors to form longer molecular chains in the presence of laccase as a catalyst. In this study, soil was treated with different lignin contents (8%, 10%, and 12%) under different water/lignin ratios (0.4, 0.6, 0.8, and 1.0) and then cured in air or heat for various durations (4, 7, 14, and 21 days). Specimens treated by lignin and polymerized lignin were tested to determine the unconfined compression strength (UCS). For the specimens treated by lignin, the results showed that a higher lignin content can improve the UCS if the specimens were cured in the air, and heat curing can improve the strength by more than 40% compared with the ones cured in the air. The tests indicated that excessive lignin content would cause bleeding that prevented further increase of the strength. Moisture was identified as a main factor causing loss of strength of the treated specimens. Polymerization appears to be an effective approach to further improve the strength. Polymerization decreased the hydrophilicity and increased the length of molecular chains, which greatly enhanced the strength of treated soil. According to the results, a combination of polymerization and heat curing would provide the highest strength, which was approximately 10 times higher than the ones treated with regular lignin and cured in air.

Wood is classified as one of the most common building materials due to its diverse nature. Casuarina is considered one of the fast-growing trees in relatively arid countries such as Egypt. This paper aims to test the mechanical properties for the most two common species of Casuarina in Egypt, which are glauca and cunninghamiana. This research mostly focused on testing these two species for compression parallel to the grain, compression perpendicular to the grain, and static bending; tension parallel to the grain, tension perpendicular to the grain and cleavage tests were only tested on glauca because cunninghamiana was excluded after the first three tests due to the high variability and inconsistency in its results. All the tests were done according to the current standards for wood. The results show that the properties of the glauca species of casuarina wood are promising because it has sufficient strength that could enable it to be used in several structural applications.

Microbially induced calcite precipitation (MICP) is a sustainable biological ground improvement technology that is capable of improving the engineering properties of soil. A laboratory study was conducted to investigate the influence of some key environmental parameters on the long-term engineering performance of MICP-treated sandy soil, including wet-dry cycles, freeze-thaw cycles, and acid rain conditions, and to study the effect of enhancement through fiber reinforcement and multiple MICP treatments. Experimental results indicated that durability of MICP-treated soil was weak in wet-dry cycles, freeze-thaw cycles, and acid rain conditions. The unconfined compression strength (UCS) of MICP-treated soil had nearly 80% reduction after one wet-dry cycle, 58% reduction after 15 freeze-thaw cycles, and 83% reduction after 15 days immersed in acid rain solution with the pH of 3.5. Fiber reinforcement mainly enhanced the ductility of MICP-treated samples. The failure strain of fiber-reinforced samples reached 1.6% compared with unreinforced samples of 0.4% after 5 wet-dry cycles. Multiple treatments enhanced the durability of MICP-treated samples. The UCS of multiple MICP-treated samples had no significant reduction after wet-dry and freeze-thaw cycles. For quadruple MICP-treated samples, a 51.9% UCS still remained after 15 days immersed in acid rain solution with the pH of 3.5.

The influence of maximum aggregate size on the bond-slip behavior between concrete surfaces and carbon fiber–reinforced polymer (CFRP) sheets was investigated. A total of 78 concrete prisms ($150\times 150\times 200\mathrm{mm}$) were cast, and six concrete mixes were prepared with different maximum aggregate sizes (25, 19, 12.5, and 9.5 mm) and concrete compressive strengths (20, 30, and 40 MPa). The specimens were reinforced with CFRP sheets and tested under a double-shear test. CFRP sheet strips with different lengths, widths, and numbers of layers were externally bonded to the concrete prisms using epoxy. The effects of each factor on the bond behavior were investigated through the bond stress versus slip curves and failure modes. Experimental results showed that the maximum aggregate size highly affected the bond behavior. Both the bond strength and maximum slippage increased as the maximum aggregate size used increased from 9.5 to 19 mm. After 19 mm, the aggregate size no longer had significant influence on the bond strength. The main failure mode for specimens was debonding at the interface between the fiber sheet and concrete surface. The bond strength model proposed in the literature has been modified to consider the maximum aggregate size. The modified bond strength equation is capable of accurately predicting the bond strength.

The objective of this paper was to evaluate the effect of using rice husk ash (RHA), crumb rubber powder (CRP), and combination of RHA and CRP (RHA/CRP) on the high-temperature performance of asphalt binder. Different dosages of RHA (1%, 4%, and 7%) and CRP (5%, 10%, and 15%) by weight of asphalt binder were used to prepare modified asphalt. Various experimental tests (penetration, ring and ball test, rotational viscosity, dynamic shear rheometer, and multiple stress creep recovery) were conducted. The obtained results indicate that adding RHA and CRP affected the high-temperature performance of asphalt binder positively by increasing softening point, penetration index, viscosity, complex modulus, rutting factor, failure temperature, and percent recovery, reducing penetration, phase angle, as well as nonrecoverable creep compliance ($J_{nr}$). Furthermore, the asphalt binder modified with RHA/CRP demonstrated better performance compared to asphalt binders modified with RHA or CRP.

Developing appropriate experiments to characterize the rutting potential of an asphalt binder will aid in suitable selection of asphalt binders for a location, depending on the prevailing temperature and loading conditions. This study is an attempt to develop a ranking parameter for the high-temperature performance of asphalt binders that can explain the effect of temperature, stress levels, and short-term aging. Six different asphalt binders comprising conventional, warm mix modified, and polymer modified binders were used in the study. A multiple stress creep and recovery (MSCR) test was conducted at 40°C, 50°C, 60°C, and 70°C using four different stress levels of 3.2, 5, 8, and 10 kPa. The test was conducted on unaged and rolling thin-film oven (RTFO) aged conditions. The Arrhenius equation was used to model the variation of unrecoverable creep compliance, $J_{nr}$, with temperature at different stress levels. It was found that, irrespective of stress level and aging condition, the Arrhenius equation can be successfully used to model the variation of $J_{nr}$ with temperature. The activation energy, $E_a$, in the Arrhenius equation was found to be a useful parameter to explain the rutting characteristics of the asphalt binders. A new ranking parameter $\overline{E_{\mathrm{a}}}/({\overline{J}}_{nr,\text{Maximum}\text{Temperature}}\times \overline{m})$ was defined in the study and it can be successfully used to quantify the high-temperature performance of asphalt binders. An aging index was also proposed using the ranking parameter to explain the effect of short-term aging on the rutting susceptibility of the binders. The comparative analysis of the asphalt binders led to a conclusion that elastomeric polymer modified binder, $\mathrm{PMB}\text{-}\text{S}$, outperforms all the other asphalt binders in both unaged and aged conditions. It is envisaged that such ranking system will ensure the true behavior of asphalt binders under variation of temperature and load conditions in the pavement.

The fatigue performance of Solution Road RomixSoilfix (SRX)-stabilized crushed rock material (SRX-CRM) has rarely been studied. This study investigated the fatigue performance of SRX-CRM obtained through vertical vibration compaction. The fatigue equations of SRX-CRM are established. In addition, the fatigue performances of SRX-CRM and cement-stabilized macadam (CSM) are compared. Results show that under a 50% failure probability, the regression coefficient $a$ of the fatigue equations varies from 0.12 to 0.16, and the regression coefficient $b$ varies from 0.0573 to 0.0507. The fatigue properties of SRX-CRM considerably increase from 0.50% to 0.75% with the SRX content, especially under high stress levels. The fatigue performance of SRX-CRM is evidently better than that of CSM.

This work evaluated the performance and impacts of several agro-based anti-icers along with two traditional chloride-based anti-icers (23% by weight NaCl brine and its beet juice blend). A statistical design of experiments (central composite design) was employed for developing anti-icing liquids consisting of cost-competitive chemicals such as renewable agro-based compounds (Concord grape extract and glycerin); sodium chloride; sodium metasilicate; and sodium formate. The following experimentally obtained parameters were examined as a function of the formulation design: ice-melting capacity at $-3.9°\mathrm{C}$, splitting tensile strength of portland cement mortar samples after 10 freeze-thaw/deicer cycles, corrosion rate of C1010 carbon steel after 24-h immersion, and impact on low temperature performance of asphalt binder. One viable formula (the best performer) was tested for thermal properties by measuring its differential scanning calorimetry (DSC) thermograms and other properties (friction coefficient on anti-iced asphalt pavement, pH, oxygen demands). These laboratory data shed light on the selection and formulation of innovative agro-based snow and ice control chemicals that can significantly reduce the costs of winter road maintenance operations.

In order to be used as paving asphalts, bio-oil modified asphalt binders (biobinders) should provide adequate functionality over a wide temperature spectrum in resisting permanent deformation and fatigue cracking. The objectives of this study were to evaluate the rheological behavior and performance of biobinders under intermediate and high temperatures, and to assess the effects of bio-oil modification under a variety of oxidative aging conditions for aging susceptibility of the biobinders. The rheological and performance characterization was based on frequency sweep, linear amplitude sweep, elastic recovery, and multiple stress creep recovery tests. Experimental results indicated that an increase in the bio-oil percentage provided improved fatigue cracking performance but reduced rutting resistance and elastic recovery potential at all aging levels. Oxidative aging produced the reversed effects for both the control and biobinders. Use of bio-oil appeared to abate the aging susceptibility in terms of fatigue cracking resistance, but also rendered the asphalt binders less resistant to aging with regard to elastic recovery potential. The aging susceptibility of the petroleum asphalt and biobinders were similar concerning the rutting resistance. The correlations among the obtained performance parameters verified that the fatigue cracking resistance, rutting resistance, and elastic recovery property of the biobinders at all aging levels were generally in line with those of the petroleum asphalt, and that the biobinders could be potentially utilized as sustainable paving asphalts.

This study presents an experimental investigation on the microstructure and the hydraulic properties of a coarse-grained soil used in high-speed railway track bed at various compaction degrees. A large-scale infiltration column was adopted to study the soil water retention curve (SWRC) and the hydraulic conductivity. The microstructure of the fines in the samples was investigated by scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) tests. The results reveal the existence of a characteristic pore diameter as 12.1 μm, separating two pore groups: macropores (pore $\mathrm{diameter}\ge 12.1\mathrm{\mu m}$) and micropores (pore $\mathrm{diameter}<12.1\mathrm{\mu m}$). According to the Young-Laplace law, this characteristic pore diameter is consistent with the matric suction (negative pore water pressure, the difference value between the air pressure and the water pressure) value of 24.0 kPa. This value is also the characteristic matric suction ${\psi }_{cha}$ identified from the infiltration column test. When the matric suction is lower than ${\psi }_{cha}$, the hydraulic properties of this soil are primarily affected by the macropores. As the compaction degree increases, the macropore content decreases, leading to the decreases of the water retention capacity and the hydraulic conductivity in this suction range. However, with the matric suction higher than ${\psi }_{cha}$, the micropores more significantly affect the hydraulic properties. As the compaction degree increases, the micropore content increases, resulting in the increase of the water retention capacity and the hydraulic conductivity at this suction state.

Self-compacting concrete (SCC) is a cementitious composite that serves complex formworks without mechanical vibrations. SCC has been widely used in modern concrete structures because of its superior performance, including excellent deformability and high resistance to segregation. A new kind of SCC, called self-compacting rubberized concrete (SCRC), is developed when crumb-rubber aggregates from waste tires are blended with different fractions in SCC to replace part of traditional aggregates; this developed SCRC achieves a better economic benefit and recycling of wasted tires. Meanwhile, polypropylene and steel fibers are also used in SCRC to improve the mechanical properties, especially at elevated temperatures. In this study, eight polypropylene and steel-fiber-reinforced SCRC mixture designs were produced. Slump-flow and J-ring experiments were performed to investigate the properties of fresh SCRC (flowability, flow speed, filling ability, and passing ability). The mechanical properties of hardened SCRC (compressive strength, tensile strength, and modulus of elasticity) after 28 days of curing were also tested. In addition, high-temperature resistance for SCRC is measured as the essential performance parameter, including mass loss, spalling distribution, and residual mechanical performance at 100°C, 300°C, and 600°C. The 0.25% optimum fiber ratio for polypropylene fiber and the 0.75% optimum steel-fiber ratio in SCRC were determined to obtain high-temperature resistance for hardened and fresh SCRC.

The compressive response of confined concrete greatly depends on the mechanical properties of the confining material. Based on these materials, various stress–strain models have been proposed in the past. Among these materials, the use of fiber reinforced–polymer (FRP) composites is now considered a promising solution to improve the overall behavior of confined concrete. New materials are being developed and used in seismic strengthening/retrofitting applications. Without experimental evidence, applicability of existing stress–strain models to new confining materials with different mechanical properties remains questionable. In this paper, existing stress–strain models which were mostly developed for steel and other FRPs with high elastic modulus and low rupture strain were assessed in predicting the ultimate condition of concrete confined by polyethylene terephthalate (PET) FRP, which is a newly developed material with low elastic modulus and large rupture strain (LRS). The ultimate strength was predicted well by some of these models; however, the ultimate strain could not be well predicted. Regarding the prediction of ultimate strain, some of those models which considered the axial strain capacity of FRP performed relatively better. Considering this discrepancy, a new simple stress–strain model is proposed for PET FRP–confined concrete, which not only considers the ultimate conditions but also the control points in the course of stress–strain path. Based on these control and ultimate points, stress–strain curves were generated using a well-known base curve. Finally, the proposed model was verified in predicting the ultimate condition of existing test data of PET FRP–confined concrete.

This study investigated the properties of colloidal nanoalumina (CNA)-blended cementitious mixtures in the presence of calcite to promote better understanding of the enhancing mechanisms of nanoalumina in cementitious materials through experimental investigation and thermodynamic calculation. The rate of heat evolution, compressive strength, connected pore structure, and chloride binding capacity were investigated. The results show that CNA can accelerate cement hydration at early age, and therefore improve the 1-day strength of blended mixtures. The strength at 28 and 56 days can be maximized with 1% by weight CNA addition, but considerably reduced with 5% by weight CNA. Different from the mechanical properties, the connected pore structure and chloride binding capacity are improved straightforwardly with CNA addition, which benefits the ability to resist chloride attack. The experimental and modeling results demonstrate that CNA addition benefits the generation of carboaluminate, which has high efficiency to fill voids due to its higher volume, thus densifying the microstructure as well as improving the chloride resistance. However, these aluminate-ferrite-monosubstituent (AFm) phases demonstrate little cementing capacity relative to calcium silicate hydrate (C─ S─ H) gels, thus resulting in an obvious decrease of strength with a high amount of CNA addition even though the microstructure is further densified.

The expanded distinct element method based on a strain strength criterion was applied herein with the aim of analyzing and comparing the cracking behaviors of rock-like specimens with single flaws under uniaxial and biaxial compressions. The cracking characteristics in uniaxial and biaxial compressions were compared and the effects of confining pressure on the tensile/shear behaviors were analyzed. The confining pressure obviously changed the boundary condition and the cracking behaviors in biaxial compression. The initiation stress, the peak strength, and the number of shear cracks in biaxial compression were obviously larger than in uniaxial compression. The confining pressure affected the initiation and propagation of the secondary cracks, the failure mechanisms, and the distribution of horizontal displacement fields in a large extent. The initiation and propagation of the tensile cracks were inhibited by the confining pressure. An increase in confining pressure had no obvious effects on the initiation time and the propagation rates of the shear cracks but mainly affected the numbers of shear cracks.

To quantitatively evaluate the effect of diatomite, basalt fiber, and their interaction on high- and low-temperature performance, as well as viscoelastic performance of asphalt, the softening point tests, Brookfield viscosity tests, dynamic shear rheometer (DSR) tests, and bending beam rheometer (BBR) tests were conducted. Based on DSR results at different temperatures, the shift factors deduced by a new method were adopted to plot master curves of asphalt. The Christensen-Anderson-Marasteanu (CAM) model was then used to fit the master curves and analyze the effects of different contents of diatomite and basalt fiber on the dynamic viscoelastic performance of asphalt. Then, the effect of the interaction between diatomite and basalt fiber on the performance of asphalt is quantitatively evaluated by two-way ANOVA. To further investigate and verify the mechanism of asphalt performance influenced by diatomite and basalt fiber, scanning electron microscope (SEM) tests were carried out. Results revealed that diatomite, basalt fiber, and their interaction had a significant effect on the high- and low-temperature performance, shear resistance, fatigue cracking resistance, and temperature sensitivity of asphalt. However, diatomite had the most significant effect on high-temperature performance, shear resistance, fatigue cracking resistance, and temperature sensitivity, while basalt fiber had the most significant effect on low-temperature performance. The research can provide a useful reference for the practical application of diatomite and basalt fiber in road engineering.

The research focuses on strength efficiency of rotary kiln metakaolin and flash metakaolin in concrete. The Smith and Bolomey modified model is used to develop efficiency factor $(\mathit{k})$ for calculating strength efficiency in reference to pozzolan content and relative strength. The present study shows that as the replacement percentage of metakaolin increases (up to 30%), the efficiency of metakaolin modified concrete decreases. Replacement of ordinary Portland cement (OPC) in both mixtures with up to 30% rotary-calcined metakaolin (RMK) and up to 30% flash-calcined metakaolin (FMK) showed an increase in strength properties as compared to control concrete after curing age of 14 days. The FMK blended concrete resulted in improved values of $\mathit{k}$ as well as enhanced strength properties as compared to RMK blended concrete. Workability for the concrete blended with FMK was higher in comparison to RMK. The significant changes in $\mathit{k}$ values were observed for both the materials after 28 days of curing at all replacement percentages.

The width of microcracks of the interfacial transition zone (ITZ) in rubber concrete exposed to sulfate attacks was investigated. The ITZ affects the mechanical properties of concrete to a certain extent. Therefore, the study of ITZ microstructure can provide a theoretical basis for the mechanical properties of rubber concrete. Specimens with 0%, 10%, and 20% replacement by volume of fine aggregates with rubber were exposed to 5% sodium sulfate solution. The effects of rubber particle size (i.e., 5–10, 10–20, 30–50, and 50–90 meshes) on microcrack width were considered. Ordinary concrete without rubber was added as a control. The microcrack width of the ITZ in composites was observed in the test, in which approximately 27 scanning electron microscopy images were obtained from each mixture. With the same rubber particle size, the ITZ microcrack width of concrete with 20% rubber was larger than that of concrete with 10% rubber content. With the same rubber content, the microcrack width increased as rubber particle size increased.

The strength of wooden boards is related to its natural defects and the ability of a stress wave to propagate around them. Anisotropy, heterogeneity, and the strong moisture dependency of wood make it difficult to predict its strength. Covering the ordinary quality range of wood, a numerical simulation model was developed for strength prediction of timber, and 250 boards were numerically simulated. In this study, by virtually reconstructing a three-dimensional (3D) geometrical model of each case based on the surface information of the knots, and by predicting the fiber patterns, the material properties of wood were virtually predicted. Thus, the strength predictions were done solely based on the surface information of the knots. Strength variation in a knot-free board is only dependent on the variation of the actual density of the board. As the actual density of wood may not be available under different environmental conditions for measuring the dynamic modulus of elasticity (${MoE}_{dyn}$), the average density of each set was used as one of the only input parameters for simulations. The resonance kind stress wave propagation and its return were calculated in the reconstructed boards. Numerical results of the finite-element (FE) stress wave analysis were used in a linear regression analysis for prediction of the tensile strength based on the information of the calculated time of the stress wave. The predicted results were benchmarked against the measured values in the laboratory. Performing a multiple regression analysis, the virtual results provided much higher strength predictions than the geometrical parameters available from scanners. However, strong knot interactions in lower-quality boards also affect the strength predictions. This study provides a comprehensive system (starting from the geometrical reconstruction of the boards to the virtual analysis for calculation of the virtual ${MoE}_{dyn}$) for the strength prediction of wood that is based solely on the surface images. The developed model makes it possible to predict the tensile strength of timber with relatively high accuracy, which is approximately at the same level as current grading machines.

Rolling shear (RS) strength may govern load-carrying capacity of cross-laminated timber (CLT) subjected to high out-of-plane loading because high RS stresses may be induced in cross layers and wood typically has low RS strength. This study investigates RS strength properties of non-edge-glued CLT via experimental testing (short-span bending tests and modified planar shear tests) and numerical modeling. CLT specimens with different manufacturing parameters including two timber species (New Zealand–grown Douglas fir and Radiata pine), three lamination thicknesses (20, 35, and 45 mm), and various lamination aspect ratios (4.1–9.8) were studied. The lamination aspect ratio was found to have a substantial impact on RS strength of CLT. Higher aspect ratios led to a significant increase of RS strength, and an approximately linear relationship could be established. With similar lamination aspect ratios, the Radiata pine CLT had higher RS strength than the Douglas fir CLT. The two different test methods, however, yielded comparable RS strength assessments. Numerical models were further developed to study the influence of the test configurations and gaps in the cross layers on stress distributions in the cross layers. It was also found that the compressive stresses perpendicular to the grain in cross layers had negligible influence on the RS strength evaluations.

Experimental investigation on the cohesive–frictional shear behavior of soft-brick masonry under various levels of applied compression is reported. The progressive failure in the bed joint produced by a crack propagating along the brick-mortar interface is evaluated for masonry made with a soft brick and mortars of different strengths. The load response indicates a cohesive-frictional-type interface response with a cohesive interface bond and residual frictional resistance. The fracture planes after failure depend on the type of mortar used and the applied compression. Failure surfaces are rougher in cement-rich mortars, and the roughness increases with the level of confinement. A cohesive–frictional interface model is developed and calibrated using experimental responses. The cohesive–frictional parameters obtained from the experiments vary with the type of mortar and the level of compression. The peak cohesive shear stress and cohesive fracture energy increase with the level of compression applied normal to the shear plane. The interface with the cement-rich mortars exhibit a more pressure-sensitive response. A higher cohesive peak stress is obtained for cement-rich mortar. Cement-rich mortar exhibits a more brittle response with smaller displacements at the initiation of crack and at complete separation.

Lithium slag (LS), which is a byproduct of lithium salt production, has never been reported in alkaline activation studies. In this work, either characteristics of reaction products of alkali-activated lithium slag (AALS), such as phase compositions, microstructure, specific surface area, and water content, or the pore solution composition in AALS at an early reaction age is investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the phases and microstructural morphology of AALS samples at typical reaction times ($\mathrm{t}=10\min$, 30 min, 1 h, 3 h, 6 h, 12 h, and 24 h). In particular, the combination of Fourier transformation infrared (FT-IR) spectroscopy and ${}^{29}\mathrm{Si}$ solid-state nuclear magnetic resonance (${}^{29}\mathrm{Si}$ NMR) were used to analyze the bonding linkage and the adjacent coordination structure of ${}^{29}\mathrm{Si}$ in LS and intermediate products of AALS. The results indicate that the Si─ O─ Si bond decreases while the Si─ O─ Al bond increases with alkaline activation reaction (AAR) enhancing and the chemical environment of Si preferred to ${\mathrm{Q}}^4(3\mathrm{Al})$ and ${\mathrm{Q}}^4(2\mathrm{Al})$ units compared with original LS, of which has more ${\mathrm{Q}}^4(1\mathrm{Al})$ and ${\mathrm{Q}}^4(2\mathrm{Al})$ units. Moreover, the composition of the pore solution was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). This paper reveals the evolution of AALS from multiple perspectives and may be of great significance for solid waste utilization.

Cement modification of soils has been widely practiced for the last few decades. Recently, cement has become a more economical binder to modify in situ subgrade soil because other binders, such as fly ash, have become less available and therefore their prices have gone up significantly. In addition, a much higher percentage of fly ash needs be used when compared with cement to achieve the same subgrade strength and stiffness. However, cement-modified subgrade may have an issue with shrinkage cracking, which can eventually reflect through the asphalt pavement layers to the surface after construction. For some subgrade soils, a high cement content is needed to meet the unconfined compressive strength requirement without jeopardizing durability. A higher cement content will result in higher shrinkage cracking potential. To overcome this problem, microcracking technology has been developed and adopted in the field. This technology involves recompaction of cement-modified soil (CMS) with a roller 24–48 h after initial compaction to induce microcracks in the CMS and minimize the potential for large shrinkage cracks. Microcracking of CMS is not expected to significantly reduce the strength and stiffness of CMS, but it is expected to increase its permeability and reduce the potential for large shrinkage cracks. Unfortunately, the procedure to simulate microcracking of CMS in the laboratory and evaluate its effect on properties of CMS has not been established yet. This note documents the development of such a procedure and discusses the effect of microcracking on the properties (strength and modulus) of CMS specimens.